This invention relates to a light emitting device, a method of fabricating a light emitting device, an integrated circuit comprising a light source and a method of coupling emitted light out of a device comprising a light source.
It is known that forward-biased silicon pn-junctions emit light in a narrow band around 1.1 μm, but this radiation can only be electrically switched at speeds up to a few hundred kHz, which makes it unsuitable for optical communication systems.
On the other hand, reverse-biased avalanching silicon pn-junctions emit light in a wide band from 350 nm to 1.7 μm, with a peak at about 700 nm and can be switched at GHz speeds. However, devices with these junctions have a lower electroluminescent efficiency than devices with forward-biased silicon pn-junctions.
While standard CMOS silicon semiconductor manufacturing processes are used worldwide for many microelectronic devices, the devices are relatively inefficient at generating light and it is difficult to couple generated light out of a CMOS integrated circuit (IC). A first or top face of the CMOS IC is usually covered with various layers of insulating silicon dioxide (SiO2) and metal interconnect with usually uneven topographies. These layers and topographies inhibit the out-coupling of light from the IC and misdirect and distort the external radiation pattern of the exiting light.